The invention addresses a method for optimizing ultrasonic transmit and receive pulses, particularly for ultrasound imaging, wherein transmit pulses are generated from ultrasonic pulse contributions of each of a plurality of electroacoustic transducers, which are grouped in an array and are individually triggered by electric excitation signals, the excitation signal being applied to each individual transducer of the array with a predetermined delay with respect to the application of the excitation signal to the other transducers, and a weight being applied to the excitation signal of each transducer for increasing/decreasing the amplitude of the excitation signal and, as a result, the acoustic signal generated by the transducer.
In prior art insonification and ultrasonic pulse generation methods for ultrasonic imaging, each pulse results from ultrasonic pulse contributions of a certain number of electroacoustic transducers which are individually excited to transmit the corresponding acoustic pulse at different times, i.e. with predetermined delays relative to each other, to generate a comprehensive pulse which is focused on a predetermined scan line or band in the direction of the body or object under examination, and at a predetermined penetration depth within said body or object under examination.
In addition to said focusing, the application of amplitude attenuating/increasing weights to the individual acoustic pulse contributions provided by transducers is known, in order to obtain beam patterns, i.e. pulse fronts having a narrow main lobe, having a predominant amplitude as compared with side lobes. This has the purpose of reducing insonification in regions of the body or object under examination that are close to those on which the ultrasonic transmit pulse is focused and of reducing artifacts in images. Essentially, the side lobes generate reflection pulses from the areas adjacent to pulse focusing areas, and thereby contaminate or distort to a certain extent the resulting image by superposition of such pulses upon the reflection pulses deriving from the main lobe and from the ultrasonic pulse focusing area on the body or object under examination.
Nevertheless, in prior art no consideration is given to the problem that such optimization process does not account for the effects on mechanical pressure distribution in the body or object under examination, which is not optimal in itself, and becomes even less homogeneous in the focusing region, as a result of the ultrasonic pulse optimization process as described above.
The mechanical pressure that is exerted in the body or object being examined also has a certain importance, an excessive mechanical pressure potentially causing the structure of the material of the body or object under examination to break. Such effect is particularly undesired in the field of biomedical imaging, the tissues of the body or object under examination being frequently permeated with contrast agents to enhance visibility of non echogenic tissues. These contrast agents are made of microspheres or microbubbles, which have a nonlinear reflection behavior and reflect the acoustic signal at a frequency that is different from that of the incident transmit pulse, thereby allowing to image structures of non echogenic materials or tissues.
Contrast agents are particularly responsive to the mechanical pressure exerted by acoustic insonification pulses and may be destroyed when such mechanical pressure exceeds predetermined limits.
Essentially, when considering the mechanical pressure profile generated along the scan line on which the ultrasonic pulse is focused, at depths different from the focusing depth, the mechanical pressure value is found to change with depth. Since contrast agents may be located along a scan line at different positions as compared with the ultrasonic pulse focusing depth, prior art methods cannot ensure that the ultrasonic pulse has the right mechanical pressure in the area that is permeated with contrast agents, and it is further not easy to predict if such pressure will be lower or higher than the maximum allowed pressure to prevent contrast agent destruction. Also, regarding the beam pattern, prior art methods cannot ensure that the latter will be constant or substantially constant or anyway that it will maintain a good quality as the penetration depth of the ultrasonic pulse within the body or object under examination changes.